Cop2 loaded red phosphorus, preparation and use of the same

ABSTRACT

Disclosed are a photocatalyst of CoP 2  loaded red phosphorus, a preparation method thereof, and a method for photocatalytic hydrogen production from water under visible light irradiation over the photocatalyst of CoP 2  loaded red phosphorus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional PatentApplication No. 61/700,751 as filed on Sep. 13, 2012. The disclosure ofthe provisional application is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present application relates to a photocatalyst, a preparation methodand a use thereof.

TECHNICAL BACKGROUND

Hydrogen is an important industrial raw material and a special gashaving reducibility in petrochemical and fine organic synthesisindustries. It is also used in aerospace and viewed as the energy sourceof the future, due to its high combustion enthalpy (−286 kJ/mol).Currently, the technologies for hydrogen production are mainly steamreforming from hydrocarbons, electrolysis and thermolysis. Hydrogen-gasas a fuel to drive vehicles such as buses, cars and the like is not usedvery often because the technique necessary to generate energy out ofhydrogen is very expensive.

Solar-induced photocatalytic hydrogen production from water is a cleanand renewable source of energy, and has been considered as a promisingway to alleviate this problem. Under irradiation, photogeneratedelectrons from a photocatalyst could reduce water to hydrogen. Thistechnology is an environmentally friendly process and promising toproduce hydrogen in a low cost. Besides, hydrogen can be produced insitu and does not need to be transported.

However, the efficiency and the application of photocatalytic hydrogenproduction are limited by the narrow absorption of semiconductor and theneed of expensive co-catalyst, such as Pt. Even though great effortshave been made to develop new photocatalysts and co-catalysts, theseproblems still could not be solved. Accordingly, a novel and desirablephotocatalyst with a suitable conduction band energy for transferringphotogenerated electrons to water is needed.

SUMMARY

In one aspect, the present application provides a photocatalyst of CoP₂loaded red phosphorus.

In another aspect, the present application provides a method forpreparing a photocatalyst of CoP₂ loaded red phosphorus, comprising:

a) growing CoP₂ from a red phosphorus in water; and

b) treating the CoP₂ loaded red phosphorus at a temperature ranging from450° C. to 650° C.

In another aspect, the present application provides a method forphotocatalytically producing hydrogen from water in the presence of asacrificial agent over a photocatalyst of CoP₂ loaded red phosphorus.

In another aspect, the present application provides a use of CoP₂ as aco-catalyst for a red phosphorus.

CoP₂ loaded red phosphorus as provided in the present application is aphotocatalyst with broad visible light absorption and highphotocatalytic efficiency for hydrogen production from water. Theabsorption band edge of red phosphorus can be up to 700 nm, which can bedriven by visible light. When used for hydrogen production from water,the performance of CoP₂ can be up to 6 times higher compared with thecommon co-catalyst of Pt under the same conditions. Moreover, as anon-noble metal co-catalyst, the price of CoP₂ is about 200 times lowerthan that of Pt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows TEM image of CoP₂ loaded red phosphorus prepared inExample 1.

FIG. 1 b shows another TEM image of CoP₂ loaded red phosphorus preparedin Example 1.

DETAILED DESCRIPTION

In the following description, certain specific details are included toprovide a thorough understanding of various disclosed embodiments. Oneskilled in the relevant art, however, will recognize that embodimentsmay be practiced without one or more of these specific details, or withother methods, components, materials, etc.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, which is as “including, but not limited to”.

Reference throughout this specification to “one embodiment”, or “anembodiment”, or “in another embodiment”, or “some embodiments”, or “insome embodiments” means that a particular referent feature, structure,or characteristic described in connection with the embodiment isincluded in at least one embodiment. Thus, the appearance of the phrases“in one embodiment”, or “in an embodiment”, or “in another embodiment”,or “in some embodiments” in various places throughout this specificationare not necessarily all referring to the same embodiment. Furthermore,the particular features, structures, or characteristics may be combinedin any suitable manner in one or more embodiments.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the content clearly dictates otherwise. In this application, theuse of “or” means “and/or” unless stated otherwise.

In one aspect, the present application provides a photocatalyst of CoP₂loaded red phosphorus.

In some embodiments of the present application, CoP₂ is loaded at about0.5% to about 7.0% by weight, preferably about 1.0% to about 4.0% byweight, more preferably about 2.0% to about 4.0% by weight, mostpreferably about 2.0% by weight.

In some embodiments of the present application, the red phosphoruscontained in the photocatalyst preferably is a crystalline redphosphorus.

In some embodiments of the present application, the CoP₂ loaded redphosphorus has photocatalytic activity and can be used for hydrogenproduction from water.

In another aspect, the present application provides a method forpreparing a photocatalyst of CoP₂ loaded red phosphorus, comprising:

a) growing CoP₂ from a red phosphorus in water; and

b) treating the CoP₂ loaded red phosphorus at a temperature ranging fromabout 450° C. to about 650° C., preferably about 450° C. to about 500°C., more preferably about 450° C.

In some embodiments of the present application, the step of growing CoP₂from a red phosphorus is carried out by the hydrothermal reaction of acobalt compound with a red phosphorus.

In some embodiments of the present application, the hydrothermalreaction of the cobalt compound with the red phosphorus can be carriedout at a temperature ranging from 150° C. to 200° C. for 12-24 hours,preferably about 200 ° C. for about 12-20 hours, more preferably about200° C. for about 12 hours.

In some embodiments of the present application, the cobalt compound thatcan be used includes but is not limited to cobalt acetate, cobaltchloride, potassium cobalt cyanide, and a combination thereof.

In some embodiments of the present application, the red phosphorus usedin step a) is an amorphous red phosphorus.

In some embodiments of the present application, the molar ratio of thered phosphorus to the cobalt compound used in step a) can be 50-2000:1,preferably 100-600:1, more preferably 400-600:1.

In some embodiments of the present application, a molar concentration ofthe red phosphorus in water in step a) can be 0.1-1 M, preferably0.2-0.4 M.

In some embodiments of the present application, CoP₂ loaded redphosphorus in step b) can be thermally treated at a temperature rangingfrom about 450° C. to about 650° C. for about 2 hours-about 15 hours,preferably at about 450° C. to about 500° C. for about 2 hours-about 15hours, more preferably at a temperature of about 450° C. for about 5hours-about 12 hours.

In some embodiments of the present application, CoP₂ loaded redphosphorus in step b) can be thermally treated under vacuum.

In some embodiments of the present application, the method for preparingthe photocatalyst of CoP₂ loaded red phosphorus further comprises a stepof purifying the red phosphorus before growing CoP₂ from the redphosphorus in water.

In some embodiments of the present application, the red phosphorus ispurified in water by the hydrothermal method at a temperature of about200° C. Specifically, the step of purifying the red phosphorus comprisesdispersing a commercially available red phosphorus in water to obtain asuspension, heating the resulting suspension to about 200° C. andmaintaining at the same temperature for about 12 hours to remove surfaceoxidation.

In another aspect, the present application provides a method forphotocatalytically producing hydrogen from water in the presence of asacrificial agent over a photocatalyst of CoP₂ loaded red phosphorus.

The photo-induced hydrogen production from water over the photocatalystof CoP₂ loaded red phosphorus is evaluated below. In order to increasethe efficiency of photogenerated electrons and hydrogen formation, it ispreferable to add a hole sacrificial agent during the formation ofhydrogen to aid the separation of photogenerated electrons and holes.

Accordingly, in some embodiments of the present application, thesacrificial agent that can be used includes but is not limited tomethanol, citric acid, ascorbic acid, lactic acid and a mixture thereof,preferably methanol, ascorbic acid and lactic acid, more preferablyascorbic acid and lactic acid, most preferably lactic acid.

In some embodiments of the present application, the sacrificial agentcan be used at such amount that the concentration of the sacrificialagent in water is about 1% to about 15%, preferably about 3% to about10%, more preferably about 5%. Where the used sacrificial agent issolid, such as citric acid, ascorbic acid and the like, the aboveconcentration unit is weight percentage. Where the used sacrificialagent is liquid, such as methanol, lactic acid and the like, the aboveconcentration unit is volume percentage.

In some embodiments of the present application, the photocatalyst ofCoP₂ loaded red phosphorus can be used at a catalytic amount, which canbe determined by a person skilled in the art through conventionaltechniques in the art.

In some embodiments of the present application, the hydrogen productionfrom water can be carried out under visible light irradiation. Thevisible light is in the range of from 400 nm to 750 nm.

Briefly, the present application provides the method forphotocatalytically producing hydrogen from water comprising

a) mixing the photocatalyst of CoP₂ loaded red phosphorus, thesacrificial agent and water; and

b) irradiating a mixture obtained from step a) with a visible light.

In some embodiments of the present application, the above-mentionedmixing step can be carried out by adding the photocatalyst of CoP₂loaded red phosphorus and the sacrificial agent to water or adding thephotocatalyst of CoP₂ loaded red phosphorus to a solution of thesacrificial agent in water or adding the sacrificial agent to asuspension of the photocatalyst of CoP₂ loaded red phosphorus in water

In another aspect, the present application provides a use of CoP₂ as aco-catalyst for red phosphorus. When used for hydrogen production fromwater, the optimal performance of CoP₂ as the co-catalyst is 6 timeshigher than that of the common co-catalyst, Pt.

The CoP₂ loaded red phosphorus is also characterized by X-raydiffraction (XRD), transmission electron microscopy (TEM) and UV-Visspectrophotometer, respectively, in which XRD is performed with a RigakuSmartLab X-ray diffractometer using Cu Ka irradiation (λ=1.5406 Å);transmission electron microscopy images were recorded using a CM-120microscope (Philips, 120 kV) coupled with an energy-dispersive X-ray(EDX) spectrometer (Oxford Instrument); the electron microscopy sampleswere prepared by dispersing the powder in ethanol with ultrasonicationfor 20 s; and UV-vis diffuse reflectance spectra were achieved using aUV-vis spectrophotometers (Cary 100 scan spectrophotometers, Varian).FIGS 1 a and 1 b show TEM images of CoP₂ loaded red P prepared accordingto the present application.

EXAMPLES

Embodiments of the present application are disclosed in further detailin the following examples, which are not in any way intended to limitthe scope of the present invention.

Example 1 Preparation of CoP₂ Loaded Red Phosphorus

100 mg of commercially available red phosphorus was dispersed in 15 mlof de-ionized water to form a suspension. The resulted suspension wasput into a Teflon-lined stainless autoclave, heated to 200° C. andmaintained at 200° C. for 12 h to remove surface oxidation. 1 mg ofCobalt (II) acetate tetrahydrate (purity >99.999%, available fromSigma-Aldrich without further purification) was added into 15 mL ofde-ionized water together with 100 mg of purified red phosphorus. Afterultrasonic treatment for 5 min, the resulted mixture was transferredinto a preheated oven at 200° C. and maintained at the same temperaturefor 20 h. After the hydrothermal reaction, the reaction mixture isfiltrated and the resulted powders were washed with 8 ml of de-ionizedwater and 8 ml of ethanol for three times, separately. The washedpowders were dried at 60° C. The dried powders were crystallized in avacuum tube furnace at 450° C. for 12 h. The crystallized products werewashed with 8 ml of water and 8 ml of ethanol, and then dried at 60° C.to obtain the photocatalyst of CoP₂ loaded crystalline red phosphorus.

Example 2 Photocatalytic Hydrogen Production From Water Over CoP₂ LoadedRed Phosphorus

The photocatalytic H₂ evolution experiment was carried out in a Pyrexreaction cell connected to a closed gas circulation and evacuationsystem. 50 mg of the CoP₂ loaded red phosphorus as prepared in Example 1was dispersed in 100 mL of 5 Vol % of aqueous solution of lactic acid asa hole sacrificial agent. The resulted suspension was purged with argonto remove dissolved air before irradiation. The resulted suspension wasirradiated by a 300 W xenon lamp with an appropriate cut-off filter anda water filter. The amount of hydrogen generated from photocatalyticwater splitting was measured by Techcomp GC7900 gas chromatography witha TCD detector and a capillary column (Molecular Sieve 5 Å). High puritynitrogen gas was used as a carrier gas.

Example 3 Effect of Loading Amount of CoP₂ on Hydrogen Production

CoP₂ loaded red phosphorus was prepared in the same manner as in Example1 with the exception of different amounts of cobalt (II) acetatetetrahydrate. 1 mg, 2 mg, 4 mg, 6 mg, and 8mg of cobalt (II) acetatetetrahydrate were used to prepare the CoP₂ loaded red phosphorus havingdifferent weight percentage of CoP₂, respectively. The photocatalytic H₂evolution experiments were carried out under the same conditions as inExample 2 with the exception of CoP₂ loaded red phosphorus havingdifferent weight percentage of CoP₂. The rates of hydrogen production inthe presence of different percentages of CoP₂ with 5 vol % of aqueoussolution of lactic acid as the sacrificial agent were shown in Table 1.

TABLE 1 Detailed conditions for synthesis in the presence of differentpercentages of CoP₂ Percentages The rate of H₂ Red P Co(acac)₂•4H₂O H₂OTemperature of CoP₂ production Sample (mg) (mg) (mL) (° C.) (wt %) (μmolh⁻¹ g⁻¹) S0 100 0 15 200 0 2.7 S1 100 1 15 200 0.5 54.1 S2 100 2 15 2001.0 88.0 S3 100 4 15 200 2.0 203.0 S4 100 6 15 200 3.0 174.1 S5 100 8 15200 4.0 147.0

The above results show that the photocatalytic activity of 0.5 wt % CoP₂loaded red P is 20 times as much as that of red P, and thephotocatalytic activity of 2.0 wt % CoP₂ loaded red P is 75 times asmuch as that of red P.

Example 4 Effect of Amount of Sacrificial Agent on Hydrogen Production

2 wt % CoP₂ loaded red phosphorus was prepared in the same manner as inExample 1. The photocatalytic H₂ evolution experiments were carried outunder the same conditions as in Example 2 with the exception ofdifferent volume percentages of lactic acid. The rates of hydrogenproduction in the presence of different volume percentages of lacticacid were shown in Table 2.

TABLE 2 Comparison of the rate of hydrogen production from water withdifferent volume percentages of lactic acid over 2 wt % CoP₂ loaded redphosphorus. Lactic acid (vol %) 0 1 3 5 8 10 The rate of H₂ production29.1 67.3 133.7 203.0 210.7 215.2 (μmol h⁻¹ g⁻¹)

Example 5 Effect of Different Sacrificial Agent on Hydrogen Production

2 wt % CoP₂ loaded red phosphorus was prepared in the same manner as inExample 1. The photocatalytic H₂ evolution experiments were carried outunder the same conditions as in Example 2 with the exception ofdifferent sacrificial agents. The rates of hydrogen production in thepresence of different sacrificial agents were shown in Table 3.

TABLE 3 Comparison of the rate of hydrogen production from water withdifferent sacrificial agents over 2 wt % CoP₂ loaded red phosphorusAscorbic Lactic Citric Sacrificial agents (5%)^(a) Methanol acid acidacid The rate of H₂ production 120.3 181.1 203.0 100.5 (μmol h⁻¹ g⁻¹)^(a)For methanol and lactic acid, the unit is volume percentage, forascorbic acid and citric acid, the unit is weight percentage.

Example 6 Comparison Between CoP₂ and Pt as Co-Catalysts

CoP₂ loaded red phosphorus was prepared in the same manner as inExample 1. The photocatalytic H₂ evolution experiments were carried outunder the same conditions as in Example 2 with the exception of CoP₂loaded red phosphorus having different percentages of CoP₂and Pt loadedred phosphorus having different percentages of Pt. The rates of hydrogenproduction in the presence of CoP₂ or Pt as a co-catalyst with differentpercentages were shown in Table 4.

TABLE 4 Comparison of the rate of hydrogen production between CoP₂ andPt as the co-catalyst with different percentages in the presence of 5vol % of aqueous solution of lactic acid as the sacrificial agent. wt %0.5 1 2 3 4 CoP₂ Pt CoP₂ Pt CoP₂ Pt CoP₂ Pt CoP₂ Pt H₂ ^(a) 54.0 17.688.0 33.2 203.0 30.0 174.1 28.5 147.0 26.3 ^(a)The rate of H₂ production(μmol h⁻¹ g⁻¹)

The above results show that the optimal performance of CoP₂ as aco-catalyst is even higher than that of Pt by a factor of 6. Withoutbound by any theory, this enhanced photocatalytic activity may beattributed to the coordination effect between Co atoms of CoP₂ withwater. This interaction would decrease the bond strength of O—H, andthus H₂O would be more easily decomposed after accepting thephotogenerated electrons.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A photocatalyst of CoP₂ loaded red phosphorus. 2.The photocatalyst of claim 1, wherein CoP₂ is loaded onto the redphosphorus at about 0.5% to about 7.0% by weight, preferably about 1.0%to about 4.0% by weight, more preferably about 2.0% to about 4.0% byweight, most preferably about 2.0% by weight.
 3. The photocatalyst ofclaim 1, wherein the red phosphorus contained therein is a crystallinered phosphorus.
 4. The photocatalyst of claim 1, wherein thephotocatalyst has photocatalytic activity and can be used for hydrogenproduction from water.
 5. A method for photocatalytically producinghydrogen from water comprising: a) mixing the photocatalyst of CoP₂loaded red phosphorus of claim 1, a sacrificial agent and water; and b)irradiating a mixture obtained from step a) with a visible light.
 6. Themethod of claim 5, wherein the sacrificial agent is selected from thegroup consisting of methanol, citric acid, ascorbic acid, lactic acidand a mixture thereof, preferably methanol, ascorbic acid and lacticacid, more preferably ascorbic acid and lactic acid, most preferablylactic acid.
 7. The method of claim 5, wherein the sacrificial agent isused at such amount that the concentration of the sacrificial agent inwater is about 1% to about 15% by volume, preferably about 3% to about10% by volume, more preferably about 5% by volume when the sacrificialagent is a liquid; or the sacrificial agent is used at such amount thatthe concentration of the sacrificial agent in water is about 1% to about15% by weight, preferably about 3% to about 10% by weight, morepreferably about 5% by weight when the sacrificial agent is a solid. 8.The method of claim 5, wherein the CoP₂ loaded onto the red phosphorushas about 0.5 wt % to about 7.0 wt %, preferably about 1.0 wt % to about4.0 wt %, more preferably about 2.0 wt % to about 4.0 wt %, mostpreferably about 2.0 wt % of CoP₂.
 9. The method of claim 5, wherein thevisible light is in the range of from 400 nm to 750 nm.
 10. A processfor preparing the photocatalyst of CoP₂ loaded red phosphorus of claim1, comprising: a) growing CoP₂ from a red phosphorus in water; and b)treating the CoP₂ loaded red phosphorus obtained from step a) at atemperature ranging from about 450° C. to about 650° C., preferablyabout 450° C. to about 500° C., more preferably about 450° C.
 11. Theprocess of claim 10, wherein the step a) of growing CoP₂ from the redphosphorus is carried out by a hydrothermal reaction of a cobaltcompound with the red phosphorus.
 12. The process of claim 11, whereinthe hydrothermal reaction of the cobalt compound with the red phosphorusis carried out at a temperature ranging from 150° C. to 200° C. for12-24 hours, preferably about 200° C. for 12 hours-20 hours, morepreferably about 200° C. for about 12 hours.
 13. The process of claim11, wherein the cobalt compound is selected from the group consisting ofcobalt acetate, cobalt chloride, potassium cobalt cyanide and acombination thereof.
 14. The process of claim 11, wherein the redphosphorus used in step a) is an amorphous red phosphorus.
 15. Theprocess of claim 11, wherein a molar ratio of the red phosphorus to thecobalt compound used in step a) is 50-2000:1, preferably 100-600:1, morepreferably 400-600:1.
 16. The process of claim 11, wherein a molarconcentration of the red phosphorus in water in step a) is 0.1-1 M,preferably 0.2-0.4 M.
 17. The process of claim 10, wherein the CoP₂loaded red P in step b) is thermally treated at a temperature rangingfrom about 450° C. to about 650° C. for about 2 hours - about 15 hours,preferably at about 450° C. to about 500° C. for about 2 hours-about 15hours, more preferably at a temperature of 450° C. for about 5hours-about 12 hours.
 18. The process of claim 17, wherein the CoP₂loaded red P in step b) is thermally treated under vacuum.
 19. Theprocess of claim 10, wherein the method further comprises a step ofpurifying the red phosphorus before growing CoP₂ from the red phosphorusin water.
 20. The process of claim 19, the red phosphorus is purified inwater by a hydrothermal method at a temperature of about 200° C.